State of the Art: Electronic fuzing systems for controlling projectile warheads are well known in the art. Conventionally, projectile fuzes contain either a setback generator or a reserve battery to provide power to the fuze electronics during flight. Fuze electronics may include controllers, timing circuitry, and various sensors. Additionally, the fuze electronics may include a safing and arming module to ensure that both the arming and detonation of the projectile occur only at a desired moment.
FIG. 1 illustrates a conventional explosive projectile 60 (also referred to as a warhead). As illustrated in FIG. 1, the explosive projectile 60 includes a fuze 62 and an explosive material 64 encased by a body 66. Fuze 62 may comprise, among other parts, a faze electronics module, a power source, and a safing and arming module.
Reserve batteries, which have commonly been used as a power source for fuze electronics, may include a glass ampoule with electrolytes contained therein. Upon projectile launch, ideally the glass ampoule breaks and the electrolytic fluid flows into a cell stack and produces a battery voltage that powers the fuze electronics.
FIG. 2 illustrates a conventional reserve battery assembly 20 that includes a reservoir 22 with a liquid electrolyte 24 contained therein, and a voltage producing cell stack 26. Upon launch of a projectile, inner and outer drive disks 41, 42, respectively, are moved by the acceleration forces (shown by arrow 25), and, in doing so, reservoir 22 is crushed and the electrolyte 24 is forced into cell stack 26 producing a voltage that powers an electronics module of a projectile fuze during flight. Problems associated with reserve batteries include long delay times for fuze power-up and the use of toxic materials and expensive components. Additionally, the force required to break the glass ampoule may be inconsistent, thus resulting in inconsistent unit-to-unit output energy characteristics.
Setback generators, which are also used as power sources for projectile fuzes, generate a pulse of electricity when a projectile is fired and rapidly accelerates down a launch barrel. The pulse of electricity charges a capacitor and the energy stored in the capacitor is then used to power the fuze electronics.
FIG. 3 illustrates a conventional setback generator 10 that comprises a base cup 27, a top cap 18 and an inner frame 21 that contains a woven coil 23. A magnet 12 fits within inner frame 21 and rests against the base cup 27. The magnet 12 is initially held against the base cup 27 by a thin shear disc 14. Upon the firing of a projectile, setback generator 10 is subjected to a rapid acceleration (shown by arrows 29), which causes magnet 12 to shear through shear disc 14 and move to the right (as the drawing is oriented) until it rests against the top cap 18 of the setback generator 10 assembly. This sudden movement of the magnet 12 causes the magnetic field within the setback generator 10 to decrease, which then induces a current within coil 23. Terminal post 16 conducts the induced current away from the setback generator 10 and a corresponding voltage charges a capacitor, which powers an electronics module of the fuze during flight.
Like reserve batteries, conventional setback generators suffer from high unit-to-unit variances during setback as a result of unpredictable shearing properties of any shear disc design. Conventional setback generators using a shear disc design have high ductility and thickness tolerance properties, which may cause the setback generator to experience effects of friction on the periphery of the magnet against the shear disc edges upon shearing. Additionally, setback generators implementing a shear disc design may also experience plastic deformation and stretching of the discs upon setback, rather than a complete shear of the discs. As a result, the shear disc design suffers from high unit-to-unit output variances during projectile setback. Conventional setback generators also suffer from low energy output as well as from slow response times due to inefficient magnetic circuits. Additionally, conventional setback generators have a high unit product cost due to complex component parts, and lack packaging flexibility within the fuze.
There is a need for methods and apparatuses that simplify, improve the performance of, and increase the speed of setback generators, all while reducing the unit product cost of fuze power sources.